1. Field of the Invention
The invention relates to techniques of displaying images, and more particularly to techniques of processing signals related to a display operation of images.
2. Description of the Related Art
There are known as techniques of displaying images, image display apparatuses for displaying to a viewer an image stereoscopically representing a three-dimensional object to be displayed.
One example of such image display apparatuses, as disclosed in Japanese Patent No. 2874208, is a type of image display apparatus configured such that there is disposed between a light source (e.g., a laser) for emitting a beam of light, and a scanner for two-dimensionally scanning the beam of light which has been emitted from the light source, a wavefront-curvature modulator for modulating the curvature of wavefront of the beam of light which has been emitted from the light source, to thereby project the beam of light being scanned onto the retina of a viewer's eye. This example is occasionally referred to as a retinal scanning display.
An alternative example of such image display apparatuses is a type of image display apparatus configured such that there is disposed between a screen on which an image is two-dimensionally displayed, and a viewer, a lens array capable of modulating the curvature of wavefront of light which has been emitted from the screen, per each pixel or per each group of pixels. A still alternative example is a type of image display apparatus configured to dispose an optical spatial phase modulator between such a screen and a viewer.
In any case, those examples described above include a wavefront-curvature modulator between an emitter for emitting light and a viewer's eye, allowing stereoscopic representation of a three-dimensional to-be-displayed object.
In this regard, an example of the “three-dimensional to-be-displayed object” is a to-be-displayed object containing at least one object three-dimensionally constituted. An alternative example is a to-be-displayed object containing at least one object and a background (background scene), wherein the object and the background have different distances from a viewer, irrespective of whether or not the object is constituted three-dimensionally. A still alternative example is a to-be-displayed object containing a plurality of objects, wherein these objects have different distances from a viewer, irrespective of whether or not each object is constituted three-dimensionally.
In any case, those image display apparatuses of such a type, for a three-dimensional to-be-displayed object to be represented in a stereoscopic image, employ information relating to the depths of the three-dimensional to-be-displayed object, which is to be reproduced in the image. In these image display apparatuses, the curvature of wavefront of light composing an image is modulable per each of a plurality of sub-areas into which the image is divided. This allows the curvature of wavefront of the light to be modulated in accordance with a corresponding set of depth information, per each of the sub-areas.
Each of sub-areas into which an image is divided is, in an example, one of a plurality of pixels composing an image, or one pixel group comprised of a plurality of adjacent pixels. In this example, modulation in curvature of wavefront per each sub-area would allow one field or one frame of an image, to be displayed so as to represent a plurality of regions having different depths.
Each of sub-areas into which an image is divided is, in an example, one field or frame of an image. In this example, modulation in curvature of wavefront per each sub-area would allow an image, which is composed by a plurality of fields or frames, to be displayed with different depths between a plurality of successive fields or frames. In this example, it is possible, for example, to display objects varying on a field-by-field or frame-by-frame basis, with depths varying on an object-by-object basis.
In addition, in the field of computer graphics, an image displayed on a flat screen is two-dimensional, and therefore, a three-dimensional to-be-displayed object cannot be represented in a stereoscopic image in its strict sense. However, as disclosed in Japanese Patent Application Publication No. HEI 11-25289, data for displaying an image is produced, for a three-dimensional to-be-displayed object to be perceived by a viewer as stereoscopically as possible.
For such data production, a rendering process is implemented for geometrical data representing a to-be-displayed object in a three-dimensional geometrical manner, resulting in the conversion of the geometrical data into pixel data defining display conditions per each pixel.
In this regard, the “geometric data,” for example, when a to-be-displayed object includes a three-dimensional object, means polygon data approximately representing the object in polygon. This polygon data is in the form of, for example, vector data.
On the other hand, the “pixel data” is data for representing a to-be-displayed object in a group of pixels. This pixel data includes luminance value data indicative of luminance values for each pixel on a screen; and depth data indicative of a Z-value, which is to say, information on a depth direction of the screen (i.e., a Z-value when the depth direction is defined coincident with a Z-axis direction).
In this regard, the “luminance value data” may be in the form of, for example, data indicative of luminance values in association with respective pixel coordinate-positions, or data indicative of not only the luminance values but also colors (e.g., RGB). On the other hand, the “depth data” may be in the form of, for example, data indicative of distance from a viewer's virtual or real viewpoint, in association with respective pixel coordinate-positions. Hence, specifying a targeted pixel allows a combination of the luminance value and the depth to be specified.
In the field of computer graphics, where an object to be displayed as an image on a screen includes a three-dimensional object, parts of the object, which are obscured by other parts, are therefore invisible to a viewer.
In addition, even where an object within a to-be-displayed object is two-dimensional, if the same to-be-displayed object includes a plurality of objects with different distances from a viewer, and if some of these objects are located behind other ones of these objects, the some objects, which are partially or fully obscured by the other objects, are therefore invisible to a viewer.
For these reasons, in a rendering process for a to-be-displayed object, which is to say, a content, hidden surface elimination is performed for the pixel data into which the geometrical data has directly been converted, resultantly obtaining final pixel data. The hidden surface elimination employs the depth information, which is to say, a Z-value, of an image.
For the hidden surface elimination, for example, a Z-buffer technique is used. In the Z-buffer technique, a sub-plurality of ones of a plurality of pixels composing an image to be displayed, which ones have identical display positions on a screen, are compared with each other with respect to the Z-value, to thereby determine a front-to-back order, which is to say, whether it is located nearer to or more remote from a viewer. Subsequently, the luminance value data are discarded for ones of the sub-plurality of pixels which are located more remote from the viewer, and the only the luminance value data are selected for ones of the sub-plurality of pixels which are located nearer to the viewer, accomplishing the removal of hidden surfaces in an image display.